When producing a plurality of corrugations (such as nine) in a relatively heavy sheet metal, for example ten gage, it has been customary in the past to place the steel sheet between upper and lower corrugating die shoe assemblies, each of which is provided with two fixed corrugating dies. A relatively heavy press supports the die shoe assemblies and when it is operated only two corrugations are formed in the sheet material at one time. Thus, it has been necessary to make a plurality of successive hits on the sheet metal which is being corrugated, one hit for each pair of corrugations. This procedure has had a number of disadvantages in that it is time consuming, requires a skilled press operator, and frequently produces a product which is neither dimensionally accurate nor flat. In the prior process the sheet material was drawn as well as bent by the corrugating operation. The stresses imposed upon the sheet material during the combined metal working operation frequently caused the fully corrugated sheet to be warped. Thus, a further straightening operation after the corrugating operation was frequently required. In addition, the product produced by the prior art process was not always within dimensional tolerance which prevented accurate spot welding of corrugation to mating parts.